(V) Extremely rapid ablation and in situ EBSD preparation using a femtosecond laser in the FIB-SEM

When carrying out studies of crystallography, internal strain and failure using electron backscatter diffraction (EBSD), the time-limiting factors are a combination of the speed of the EBSD detector and the time required for sample preparation – for example by vibratory polishing or focussed ion beam (FIB) polishing in-situ. The use of a femtosecond laser facilitates extremely fast sample machining and surface preparation with a small heat affected zone, precisely locating, extracting and preparing specific regions of interest.

The integration of an airlock-mounted femtosecond laser ablation chamber on the FIB-scanning electron microscope not only allows extremely rapid laser milling and access to deeply buried structures and features, but also the preparation of a surface suitable for EBSD without further time-consuming FIB milling. We further elucidate a method for this rapid single-stage preparation and show several examples of metal surfaces suitable for EBSD grain mapping, rapidly prepared using the femtosecond laser – including machining out a large region around the surface of interest to enable the appropriate electron beam and detector geometry for EBSD.

The total preparation time for each surface was under 5 minutes. While ripple-like laser induced periodic surface structures (LIPSS) are visible on the prepared surface, these do not significantly affect the quality of the EBSD pattern obtained and were minimised during method development. Focussed ion beam polishing, conducted in-situ without the sample ever leaving the microscope vacuum, can further improve the surface quality while still keeping preparation time extremely short.